Catalyst systems for cationic polymerization of isobutylene (IB) or C4 streams containing isobutylene (IB) (e.g. Raffinate 1) that can produce olefinic polymers of Mn=500-3000 with a reactive vinylidene at the terminus (HR-PIB) are of high commercial value. Catalysts based on BF3 complexes with alcohols or ethers have been used commercially, but they generally require low temperature and highly purified feed (U.S. Pat. No. 7,411,104 B2). Lewis acid-Lewis base complexes of aluminum halides or alkyl aluminum halides and ethers have also been disclosed in a range of media and with a variety of co-initiators. The initiators are primarily alkyl halides, H2O, HCl or ROH (e.g. Macromolecules 2010, 43(13), pp 5503-5507, Polymer 2010, 51, pp 5960-5969).
Getting high monomer conversions and high vinylidene in an apolar medium (suitable for commercial scale-up) using a continuous process without elaborate feed clean-up has been elusive. Catalysts that work well in a polar medium such as dichloromethane, often do not work in an apolar saturated hydrocarbon medium (Macromolecules, 2012, 43, pp 3318-3323).
One of the advances highlighted recently is that ethers with one or more electron-withdrawing groups (e.g. bis-2-chloro-ethyl ether, CEE) were particularly useful in enabling alkyl aluminum dichloride to initiate cationic polymerization in the presence of t-butyl chloride as co-initiator giving a high yield of HR-PIB (U.S. Pat. No. 9,156,924 B2). In the absence of the electron withdrawing groups, dialkyl ethers inhibited polymerization in an apolar medium (Macromolecules, 2014, 47 (6), pp 1959-1965) either because the Lewis acid-Lewis base complexes were too strong (high binding energy) or the resulting t-butyl oxonium ions were too stable. This made the rate of polymerization too slow to be commercially viable.
Even with complexes of the appropriate binding energy, it has been found that polymerization yield and terminal vinylidene content can be inconsistent and vary with the properties of the IB, and IB-containing feedstock. Applicants have found that the presence of a small amount of water surprisingly ameliorates these inconsistencies in polymerizations carried out using alkylAlCl2•CEE as catalyst and alkyl halide as initiator. The present method enables lower cost processes that can use a broader range of feedstocks. Though water itself can normally act as initiator for the polymerization of IB (US 2016/333123 A1), the presence of alkyl halide as co-initiator is necessary to control the reaction and get reasonable monomer conversions. The amount of water is also critical. Typically when water is used as an initiator for IB polymerizations, it is generally present at concentrations of 5-100, e.g 10-50 mM (US 2016/0333123 A1). However, in the presence of alkyl halide, this amount of water can cause a decrease in vinylidene end-group selectivity. On the other hand, too little water does not eliminate the inconsistent yield and terminal vinylidene content of the desired HR-PIB product.